I agree with all comments. It's all 3/4" balsa everywhere (I know from direct observation). The wet area is probobly large if it's bad enough to notice with flexing skins. If you do drill and fill besure to drill many drying holes on the inside and let them be for a year or more. Else, you'll trap water in the deck core to do it's mischief. Having recored a great deal from below I'd not do it from above, even though it is a sticky pain to recore over your head. (Takes weeks to get epoxy out of your hair!) The outer skin is thicker, provides most of the structure, and I'm just not good enough to make it look good. Cut out the bad, throw it away, recore, reglass, and paint if you like. (it's in the closet after all.)
While you're at it, and since you have the boat emptied out (see previous post), check around, see if there's more spots. Best to get it all done at once!
